1. Field of the Invention
The present invention relates to a spin-valve type magnetoresistive sensor wherein electrical resistance is changed depending on the relationship between the magnetization direction of a pinned magnetic layer and the magnetization direction of a free magnetic layer affected by an external magnetic field. More particularly, the present invention relates to a spin-valve type magnetoresistive sensor which has higher sensitivity of detection and is adaptable for high-density recording as the result of an improvement in structure and material properties of a spin-valve film laminate, as well as to a spin-valve type magnetoresistive head using the sensor.
2. Description of the Related Art
There are known spin-valve type and multilayer type as laminated structures capable of developing a GMR (Giant Magnetoresistive) effect.
FIG. 12 is a sectional view showing a conventional multilayer type GMR sensor.
The multilayer type GMR sensor has a laminated structure comprising pairs of a ferromagnetic material layer 9 and a non-magnetic electrically conductive layer 2 which are formed in plural number repeatedly from the bottom.
Generally, the ferromagnetic material layer 9 is made of a NiFe (nickelxe2x80x94iron) alloy or a CoFe (cobaltxe2x80x94iron) alloy, and the non-magnetic electrically conductive layer 2 is made of Cu (copper).
The ferromagnetic material layers 9 are positioned over and under the non-magnetic electrically conductive layer 2 in a laminated structure. Particularly, when the non-magnetic electrically conductive layer 2 is formed in a thickness on the order of 10-20 angstroms, the upper and lower ferromagnetic material layers 9 are magnetized into a single domain state in anti-parallel relation uniformly due to the RKKY interaction.
In the multilayer type GMR sensor, when the sensor is subject to a leakage magnetic field from a magnetic recording medium such as a hard disk, the magnetization direction of the ferromagnetic material layer 9 is varied to the same direction as the leakage magnetic field. A variation in the magnetization direction of the ferromagnetic material layer 9 changes electrical resistance, and this change in value of the electrical resistance results in a voltage change. The leakage magnetic field from the magnetic recording medium is detected based on the resulting voltage change.
Meanwhile, a magnetoresistance ratio (MR ratio) of the multilayer type GMR sensor amounts to the order of about 10-30% when an external magnetic field is in the range of several tens Oe (oersted) to several thousands Oe. The reason why the magnetoresistance ratio has a very large value is that there are a very large number of places where electrons scattering can occur. Further, a very strong external magnetic field is required to achieve such a high magnetoresistance ratio. This is because the magnetization direction of the ferromagnetic material layer 9 is firmly fixed in anti-parallel relation due to the RKKY interaction. It has been found from calculation of plane recording density based on the magnetoresistance ratio in the above range that the multilayer type GMR sensor is adaptable for the plane recording density up to value on the order of 100 Cb/in2. But it has also been confirmed that when a relatively weak external magnetic field on the order of several Oe is applied, the magnetoresistance ratio of the multilayer type GMR sensor becomes smaller than that of a spin-valve type magnetoresistive sensor.
FIG. 13 shows a conventional single spin-valve type magnetoresistive sensor. This sensor comprises four layers, i.e., a free magnetic layer 1, a non-magnetic electrically conductive layer 2, a pinned magnetic layer 3 and an antiferromagnetic layer 4 from the top. Numerals 5, 5 on both sides denote hard bias layers. Denoted by 6, 7 are respectively a buffer layer and a barrier layer made of non-magnetic material, such as Ta (tantalum), and 8 is an electrically conductive layer. The pinned magnetic layer 3 is selected to have a greater coercive force than the free magnetic layer 1.
Because the pinned magnetic layer 3 and the antiferromagnetic layer 4 are formed in contact with each other, the pinned magnetic layer 3 is put into a single domain state in the Y-direction and has the magnetization direction fixed in the Y-direction under an exchange anisotropic magnetic field produced by exchange coupling at the boundary surface between the pinned magnetic layer 3 and the antiferromagnetic layer 4. By heat-treating (annealing) the sensor under a magnetic field applied thereto, the exchange anisotropic magnetic field can be produced at the boundary surface between the pinned magnetic layer 3 and the antiferromagnetic layer 4.
Also, the hard bias layers 5 magnetized in the X-direction affects the free magnetic layer 1 so that the magnetization direction of the free magnetic layer 1 is uniformly set in the X-direction. In other words, since the free magnetic layer 1 is put into a single domain state in the predetermined direction by the presence of the hard bias layers 5, the occurrence of Barkhausen noise can be prevented.
In the above single spin-valve type magnetoresistive sensor, a steady electric current is applied from the electrically conductive layers 8 to the free magnetic layer 1, the non-magnetic electrically conductive layer 2 and the pinned magnetic layer 3. A magnetic recording medium such as a hard disk runs in the Z-direction. When a leakage magnetic field from the magnetic recording medium is applied to the sensor in the Y-direction, the magnetization direction of the free magnetic layer 1 is varied from the X-direction to the Y-direction. Thus, electrical resistance is changed depending on the relationship between a variation in the magnetization direction of the free magnetic layer 1 and the fixed magnetization direction of the pinned magnetic layer 3. This change in value of electrical resistance result in a voltage change. The leakage magnetic field from the magnetic recording medium is detected based on the resulting voltage change.
FIG. 14 is a sectional view showing a conventional dual spin-valve type magnetoresistive sensor.
In the dual spin-valve type magnetoresistive sensor, non-magnetic electrically conductive layers 2, 2, pinned magnetic layers 3, 3 and antiferromagnetic layers 4, 4 are formed into laminated structures on both sides of a free magnetic layer 1 at the middle in vertically symmetric relation. The magnetization direction of the free magnetic layer 1 is uniformly set in the X-direction by the presence of hard bias layers 5 magnetized in the X-direction. Also, the pinned magnetic layers 3, 3 are each put into a single domain state in the Y-direction and have the magnetization direction fixed in the Y-direction under an exchange anisotropic magnetic field produced by exchange coupling at the boundary surface between itself and the antiferromagnetic layer 4.
When a leakage magnetic field from the magnetic recording medium is applied to the sensor in the Y-direction, the magnetization direction of the free magnetic layer 1 is varied from the X-direction to the Y-direction, whereupon a value of electrical resistance is changed.
In the spin-valve type magnetoresistive sensor, when the magnetization direction of the free magnetic layer 1 is varied from the X-direction to the Y-direction, electrons existing between the free magnetic layer 1 and the pinned magnetic layer 3 and tending to move from one to the other are scattered at the boundary surface between the non-magnetic electrically conductive layer 2 and the free magnetic layer 1 and at the boundary surface between the non-magnetic electrically conductive layer 2 and the pinned magnetic layer 3. As a result, the value of electrical resistance is changed and the leakage magnetic field from the magnetic recording medium is detected based on the resulting voltage change.
The electrical resistance shows a maximum value when an angle formed between the magnetization direction of the free magnetic layer 1 and the magnetization direction of the pinned magnetic layer 3 is maximized, i.e., when these two layers are magnetized in anti-parallel relation, and shows a minimum value when the magnetization direction of the free magnetic layer 1 and the magnetization direction of the pinned magnetic layer 3 are the same. Thus, as a magnetoresistance ratio, i.e., {(maximum voltage valuexe2x88x92minimum voltage value)/minimum voltage value}, has a larger value when subject to the leakage magnetic field from the magnetic recording medium, the spin-valve type magnetoresistive sensor and hence a spin-valve type magnetoresistive head using the sensor have better characteristics.
Further, a detection output of the leakage magnetic field also greatly depends on the magnitude of a steady electric current (sensing electric current). The larger the steady electric current, the larger will be the detection output. However, if the density of the electric current flowing through the free magnetic layer 1, the non-magnetic electrically conductive layer 2 and the pinned magnetic layer 3 is too large, resulting Joule heat would give rise to problems of reducing the detection output, reliability and durability, and hence deteriorating characteristics of the spin-valve type magnetoresistive sensor. It has been confirmed that an upper limit value of the steady electric current allowing the spin-valve type magnetoresistive sensor to have satisfactory characteristics is 3xc3x97107 A/cm2. Incidentally, the upper limit value of the steady electric current can be raised by increasing the total number of layers making up the structure of the spin-valve type magnetoresistive sensor.
In the single spin-valve type magnetoresistive sensor shown in FIG. 13, electron scattering occurs at two places, i.e., the boundary surface between the non-magnetic electrically conductive layer 2 and the free magnetic layer 1 and the boundary surface between the non-magnetic electrically conductive layer 2 and the pinned magnetic layer 3. On the other hand, in the dual spin-valve type magnetoresistive sensor shown in FIG. 14, electron scattering occurs at four places in total, i.e., the two boundary surfaces between the non-magnetic electrically conductive layers 2 and the free magnetic layer 1 and the two boundary surfaces between the non-magnetic electrically conductive layers 2 and the pinned magnetic layers 3. Therefore, the dual spin-valve type magnetoresistive sensor has a larger magnetoresistance ratio than the single spin-valve type magnetoresistive sensor.
To make the sensor adaptable for high-density recording, it is important to improve the plane recording density. To improve the plane recording density, it is required to increase an output reproduced by the sensor. Further, to increase the reproduction output, it is required to raise the magnetoresistance ratio which is proportional to the reproduction output.
As mentioned above, the multilayer type GMR sensor shown in FIG. 12 can provide the magnetoresistance ratio of about 30% at maximum when the external magnetic field of several thousands Oe is applied to the sensor. However, when the external magnetic field is very weak, the magnetoresistance ratio of the multilayer type GMR sensor becomes smaller than that of the spin-valve type magnetoresistive sensor.
Further, for the multilayer type GMR sensor, it is impossible to provide the hard bias layers and suppress the occurrence of Barkhausen noise unlike the spin-valve type magnetoresistive sensor.
The reason is that if the hard bias layers are provided in the multilayer type GMR sensor, all the layers of ferromagnetic material would be magnetized uniformly in the same direction as the magnetization direction of the hard bias layers, and hence that if the external magnetic field is applied to the multilayer type GMR sensor, the electrical resistance would not be changed and the sensor could not detect the leakage magnetic field of the magnetic recording medium.
In the conventional spin-valve type magnetoresistive sensors, generally, the free magnetic layer 1 and the pinned magnetic layer 3 are each formed of, e.g., a FeNi (ironxe2x80x94nickel) alloy film, and the non-magnetic electrically conductive layer 2 is formed of, e.g., a Cu (copper) film. In the conventional single spin-valve type magnetoresistive sensor, a FeMn (ironxe2x80x94manganese) alloy film is generally used as antiferromagnetic material of the antiferromagnetic layer 4.
However, the FeMn film has a disadvantage that it is susceptible to corrosion and would be rusted soon if exposed to air containing moisture. Further, the blocking temperature for exchange coupling between the FeMn alloy film as ferromagnetic material and the FeNi alloy film constituting the pinned magnetic layer is as low as on the order of about 150xc2x0 C. This raises another disadvantage that if the temperature of a magnetoresistive head becomes high due to the heat generated by itself and the ambient temperature during operation, the exchange anisotropic magnetic field is weakened and noise in the detection output is increased.
As ferromagnetic material substitutable for the FeMn alloy, there are an IrMn (iridiumxe2x80x94manganese) alloy, a RhMn (rhodiumxe2x80x94manganese) alloy, etc.
However, films of the FeMn (ironxe2x80x94manganese) alloy, the IrMn (iridiumxe2x80x94manganese) alloy, the RhMn (rhodiumxe2x80x94manganese) alloy, etc. have properties as follows. When these alloy films are formed over the ferromagnetic material, such as an FeNi alloy, constituting the pinned magnetic layer 3, any alloy film can develop exchange coupling at the boundary surface between itself and the pinned magnetic layer 3. But those antiferromagnetic materials have such features that they are easily affected by underlying layers and their films are hard to exhibit antiferromagnetic characteristics in the vicinity of their upper surfaces. Accordingly, when the pinned magnetic layer 3 is formed over any film of those antiferromagnetic materials, it is difficult for the film of the antiferromagnetic material to develop exchange coupling.
On the contrary, films of other antiferromagnetic materials such as a CoO (cobalt oxide) alloy and a NiO (nickel oxide) alloy can each develop exchange coupling at the boundary surface between itself and the pinned magnetic layer 3 when the film is formed under the ferromagnetic material constituting the pinned magnetic layer 3. However, the films of those antiferromagnetic materials such as a CoO alloy and a NiO alloy have a feature of showing dependency in degree of crystallinity. More specifically, each film of those antiferromagnetic materials is hard to develop a satisfactory degree of crystallization in the vicinity of the boundary surface between itself and an underlying layer at start-up of a vacuum film forming process using the sputtering method, for example, attains better growth of crystals-at a position farther away from the buffer layer, and hence has a difficulty in exhibiting satisfactory antiferromagnetic characteristics in the vicinity of its lower surface. Accordingly, when the pinned magnetic layer 3 is formed under any film of those antiferromagnetic materials, it is difficult for the film of the antiferromagnetic material to develop exchange coupling.
Thus, the above-mentioned antiferromagnetic materials can develop effective exchange coupling only when formed on one side of, i.e., either over or under, the pinned magnetic layer 3. Therefore, the above-mentioned antiferromagnetic materials cannot be employed in the structure of the dual spin-valve type magnetoresistive sensor shown in FIG. 14 wherein the antiferromagnetic layers 4, 4 are formed over and under the pinned magnetic layers 3, 3.
There is known a NiMn (nickelxe2x80x94manganese) alloy as material capable of producing an exchange anisotropic magnetic field regardless of whether its film is formed over or under the pinned magnetic layer 3. This antiferromagnetic material can be formed on both sides of, i.e., over and under, the pinned magnetic layer 3 and can be used in the dual spin-valve type magnetoresistive sensor shown in FIG. 14.
To develop effective exchange coupling between a NiMn alloy film and a FeNi alloy film (pinned magnetic layer 3), however, annealing is required to be carried out at a relatively high temperature. Generally, to produce an exchange anisotropic magnetic field, it is necessary to apply a magnetic field and carry out annealing after the antiferromagnetic layer 4 and the pinned magnetic layer 3 are formed in contact relation. In the case where the antiferromagnetic layer 4 is formed of a NiMn alloy film and the pinned magnetic layer 3 is formed of a FeNi alloy film, the annealing temperature as high as about 250xc2x0 C. or above is required to develop effective exchange coupling therebetween.
But the annealing at a high temperature of about 250xc2x0 C. or above would raise a problem below. There occurs diffusion of metallic elements at the boundary surfaces of the free magnetic layer 1 and the pinned magnetic layer 3 adjacent to the non-magnetic electrically conductive layer 2 of Cu. This affects the magnetoresistive effect due to electron diffusion occurred at the boundary surface between the free magnetic layer 1 and the non-magnetic electrically conductive layer 2 and the boundary surface between the pinned magnetic layer 3 and the non-magnetic electrically conductive layer 2. The magnetoresistance ratio depending on the external magnetic field is thereby reduced.
Meanwhile, to make the sensor adaptable for high-density recording, it is important to not only improve the plane recording density, but also reduce a magnetic gap length. When the antiferromagnetic layer is formed of a NiMn alloy film, a good exchange anisotropic magnetic field cannot be achieved unless the antiferromagnetic layer must have a film thickness on the order of several hundreds angstroms. Therefore, a thickness hxe2x80x2 of the multilayered films shown in FIG. 14 is necessarily increased and hence the magnetic gap length cannot be made small. Incidentally, the free magnetic layer 1, the non-magnetic electrically conductive layer 2 and the pinned magnetic layer 3 have each a film thickness on the order of several tens angstroms.
The magnetoresistance ratio of the single spin-valve type magnetoresistive sensor is in the range of 3 to 9%. Calculation of plane recording density based on the magnetoresistance ratio in the above range results in that the single spin-valve type magnetoresistive sensor is adaptable for the plane recording density up to values on the order of 10 Gb/in2.
With the view of solving the above problems of the conventional multilayer type GMR sensor, the conventional single spin-valve type magnetoresistive sensor and the conventional dual spin-valve type magnetoresistive sensor, an object of the present invention is to provide a spin-valve type magnetoresistive sensor and a spin-valve type magnetoresistive head using the sensor, which can achieve a satisfactory magnetoresistance ratio even with a weaker external magnetic field than usually applied to the multilayer type GMR sensor, which can achieve a larger magnetoresistance ratio than achieved by the single spin-valve type magnetoresistive sensor, and which can achieve higher sensitivity and a greater detection output with a weaker external magnetic field.
Another object of the present invention is to provide a spin-valve type magnetoresistive sensor and a spin-valve type magnetoresistive head using the sensor, in which an antiferromagnetic layer is made of a PtMn (platinumxe2x80x94manganese) alloy or the like so that the temperature of heat treatment (annealing) causing the antiferromagnetic layer to develop exchange coupling can be lowered, and an effective exchange anisotropic magnetic field can be produced even with a smaller film thickness of the antiferromagnetic layer so that a magnetic gap length can be reduced.
Still another object of the present invention is to provide a spin-valve type magnetoresistive sensor and a spin-valve type magnetoresistive head using the sensor, with which the temperature of heat treatment (annealing) causing an antiferromagnetic layer to develop exchange coupling can be lowered to prevent diffusion of metallic elements and electrons at the boundary surfaces of a free magnetic layer and a pinned magnetic layer adjacent to a non-magnetic electrically conductive layer, and which can achieve a higher magnetoresistance ratio.
Still another object of the present invention is to provide a dual spin-valve type magnetoresistive sensor and a dual spin-valve type magnetoresistive head using the sensor, in which an antiferromagnetic layer is made of a PtMn (platinumxe2x80x94manganese) alloy or the like so that an effective exchange anisotropic magnetic field can be produced regardless of whether the antiferromagnetic layer is formed over or under the pinned magnetic layer.
A dual spin-valve type magnetoresistive sensor according to a first aspect of the present invention comprises non-magnetic electrically conductive layers formed over and under a free magnetic layer, pinned magnetic layers lying over one of the non-magnetic electrically conductive layers and under the other of the non-magnetic electrically conductive layers, antiferromagnetic layers lying over one of the pinned magnetic layers and under the other of the pinned magnetic layers to make the magnetization direction of the pinned magnetic layers fixed in a predetermined direction due to respective exchange anisotropic magnetic fields, and bias layers for magnetizing the free magnetic layer uniformly in a direction crossing the magnetization direction of the pinned magnetic layers, the antiferromagnetic layers being made of a PtMn (platinumxe2x80x94manganese) alloy.
According to a second aspect of the present invention, in a spin-valve type magnetoresistive sensor comprising a pinned magnetic layer having the magnetization direction fixed in a predetermined direction due to an exchange anisotropic magnetic field produced between the pinned magnetic layer and an antiferromagnetic layer, and a free magnetic layer having the magnetization direction varied with a leakage magnetic field from a magnetic recording medium, the sensor includes a first film laminate made by forming a non-magnetic electrically conductive layer and a pinned magnetic layer successively over a free magnetic layer, a second film laminate made by forming a non-magnetic electrically conductive layer and a free magnetic layer successively over a pinned magnetic layer, the second film laminate being formed over the first film laminate with an antiferromagnetic layer interposed therebetween, and electrically conductive layers for applying a steady electric current to the first and second film laminates.
The spin-valve type magnetoresistive sensor according to the second aspect of the present invention is shown in FIG. 5. This magnetoresistive sensor has such a structure that one single type spin-valve film laminate xe2x80x9cixe2x80x9d is formed on the other single type spin-valve film laminate xe2x80x9ciixe2x80x9d with the antiferromagnetic layer shared by both the film laminates. Therefore, the magnetoresistance ratio of this spin-valve type magnetoresistive sensor is larger than not only the magnetoresistance ratio (3-9%) of the single spin-valve type magnetoresistive sensor (FIG. 13), but also the magnetoresistance ratio (5-13%) of the dual spin-valve type magnetoresistive sensor (FIG. 1). Since an upper value of the steady electric current can be raised, it is also expected for this sensor to produce a higher magnetic detection output than those of the single spin-valve type magnetoresistive sensor and the dual spin-valve type magnetoresistive sensor.
According to a third aspect of the present invention, in a spin-valve type magnetoresistive sensor comprising a pinned magnetic layer having the magnetization direction fixed in a predetermined direction due to an exchange anisotropic magnetic field produced between the pinned magnetic layer and an antiferromagnetic layer, and a free magnetic layer having the magnetization direction varied with a leakage magnetic field from a magnetic recording medium, the sensor includes a first film laminate made by forming a non-magnetic electrically conductive layer and a pinned magnetic layer successively over a free magnetic layer, a second film laminate made by forming a non-magnetic electrically conductive layer and a free magnetic layer successively over a pinned magnetic layer, a third 5-layer film laminate made by forming a non-magnetic electrically conductive layer, a free magnetic layer, a non-magnetic electrically conductive layer and a pinned magnetic layer successively over a pinned magnetic layer, the third film laminate being formed over the first film laminate with an antiferromagnetic layer interposed therebetween, the second film laminate being formed over the third film laminate with an antiferromagnetic layer interposed therebetween, and electrically conductive layers for applying a steady electric current to the first, second and third film laminates.
A spin-valve film laminate of the spin-valve type magnetoresistive sensor according to the third aspect of the present invention is shown in FIG. 6. This spin-valve film laminate has such a structure that a dual type spin-valve film laminate xe2x80x9cixe2x80x9d is formed over one single type spin-valve film laminate xe2x80x9ciiixe2x80x9d with one antiferromagnetic layer shared by both the film laminates, and the other single type spin-valve film laminate xe2x80x9ciixe2x80x9d is formed over the dual type spin-valve film laminate xe2x80x9cixe2x80x9d with the other antiferromagnetic layer shared by both the film laminates. Accordingly, the magnetoresistance ratio of this spin-valve type magnetoresistive sensor is higher than that of the dual spin-valve type magnetoresistive sensor. Further, because of a higher magnetoresistance ratio and a raised upper limit value of the steady electric current, it is expected that the reproduction output of this spin-valve type magnetoresistive sensor is about three or more times that of the single spin-valve type magnetoresistive sensor.
According to a fourth aspect of the present invention, in a spin-valve type magnetoresistive sensor comprising a pinned magnetic layer having the magnetization direction fixed in a predetermined direction due to an exchange anisotropic magnetic field produced between the pinned magnetic layer and an antiferromagnetic layer, and a free magnetic layer having the magnetization direction varied with a leakage magnetic field from a magnetic recording medium, the sensor includes a 5-layer film laminate (the third film laminate) made by forming a non-magnetic electrically conductive layer, a free magnetic layer, a non-magnetic electrically conductive layer and a pinned magnetic layer successively over a pinned magnetic layer, the film laminate being stacked in multiple stages with an antiferromagnetic layer interposed between every two film laminates, antiferromagnetic layers formed each under the pinned magnetic layer lying as a lowermost layer of the film laminate at the lowermost stage and over the pinned magnetic layer lying as an uppermost layer of the film laminate at the uppermost stage, and electrically conductive layers for applying a steady electric current to the film laminates.
A spin-valve film laminate of the spin-valve type magnetoresistive sensor according to the fourth aspect of the present invention is shown in FIG. 7. This spin-valve film laminate has such a structure that the above dual type spin-valve film laminate xe2x80x9cixe2x80x9d is stacked in multiple stages with the antiferromagnetic layer shared by every two adjacent film laminates. The magnetoresistance ratio of this spin-valve type magnetoresistive sensor is higher than that of the dual spin-valve type magnetoresistive sensor. Further, because of a higher magnetoresistance ratio and a raised upper limit value of the steady electric current, it is expected that the reproduction output of this spin-valve type magnetoresistive sensor is two or more times that of the dual spin-valve type magnetoresistive sensor.
According to any of the first to fourth aspects of the present invention, the magnetization direction of the pinned magnetic layer is kept fixed under an exchange anisotropic magnetic field produced between itself and the antiferromagnetic layer, and electrical resistance is changed upon a change in the magnetization direction of the free magnetic layer resulted from an external magnetic field such as a leakage magnetic field applied from a magnetic recording medium. Therefore, a change in electrical resistance can be caused by a magnetic field of several Oe as with the conventional single spin-valve type magnetoresistance sensor. Thus, the sensor according to any aspect of the present invention is more practical than multilayer type GMR sensors wherein electrical resistance can be changed unless a magnetic field of several tens Oe to several thousands Oe is applied.
In the spin-valve type magnetoresistance sensor according to any aspect of the present invention, bias layers for magnetizing each free magnetic layer uniformly in a direction crossing the magnetization direction of the pinned magnetic layers are preferably formed on both the entire film laminate. The provision of the bias layers is effective in suppressing the occurrence of Barkhausen noise. The magnetoresistive sensor wherein Barkhausen noise is reduced by forming the bias layers can be used as a magnetic head for detecting a leakage magnetic field from a magnetic recording medium such as a hard disk. Note that the bias layers are not necessarily required in the sensor of the present invention. The sensor having no bias layers can be employed as a magnetic sensor in applications where the effect of Barkhausen noise is not problematic.
While each antiferromagnetic layer is preferably made of a PtMn (platinumxe2x80x94manganese) alloy, it may be made of a Ptxe2x80x94Mnxe2x80x94X (X=any of Ni, Pd, Rh, Ru, Ir, Cr, Fe and Co) alloy or a PdMn (palladiumxe2x80x94manganese) alloy instead of the PtMn alloy.
Preferably, the PtMn alloy has a film composition consisted of Pt in the range of 44-51 at % and Mn in the range of 49-56 at %.
In the present invention, a PtMn alloy film or any of PdMn and other suitable alloy films that have comparable properties to the PtMn alloy is used as antiferromagnetic material of the antiferromagnetic layer. Those antiferromagnetic materials can produce an effective exchange anisotropic magnetic field between the boundary surface between the antiferromagnetic and the pinned magnetic layer regardless of whether the antiferromagnetic layer is formed over or under the ferromagnetic material of the pinned magnetic layer. Therefore, a sufficient magnetoresistive effect can be achieved by using any of those antiferromagnetic materials in the dual spin-valve type magnetoresistive sensor wherein the pinned magnetic layers are arranged on both sides of the free magnetic layer in vertically symmetric relation and the antiferromagnetic layers are formed each over one pinned magnetic layer and under the other pinned magnetic layer, as well as in the spin-valve type magnetoresistive sensors of laminated structure according to the second to fourth aspects of the present invention.
Also, by using a PtMn alloy film or any of PdMn and other suitable alloy films as the antiferromagnetic layer, a sufficient exchange anisotropic magnetic field can be produced even with the heat treatment after forming the films carried out at a temperature not higher than 230xc2x0 C. Therefore, during the process of heat treatment, metallic elements and electrons are prevented from diffusing at the boundary surfaces of the non-magnetic electrically conductive layers adjacent to the pinned magnetic layer and the free magnetic layer. Consequently, a high magnetoresistance ratio can be achieved when an external magnetic field is applied.
It has been confirmed that the antiferromagnetic layer made of any of the above-mentioned materials can produce an exchange anisotropic magnetic field on the order of 300 Oe even with the antiferromagnetic layer having a very thin film thickness of about 100 angstroms. Therefore, the spin-valve film laminates of multilayer structure can be reduced in thickness.
Further, the PtMn alloy film has superior corrosion resistance to the FeMn and NiMn alloy films and is not corroded at all when subject to various solvents and cleaning agents used in the manufacture process of the spin-valve type magnetoresistive sensors and heads. Thus, the PtMn alloy film remains chemically stable during operation of the magnetoresistive heads under severe environments.
Moreover, the exchange anisotropic magnetic field produced upon contact of the PtMn alloy film and the pinned magnetic layer is thermally highly stable and has a blocking temperature as high as about 380xc2x0 C. Therefore, even if the temperature of the magnetoresistive heads is raised during the operation, it is possible to produce a stable exchange anisotropic magnetic field and stabilize accuracy of reading.
Additionally, in the present invention, a film thickness of the antiferromagnetic layer can be made smaller than conventional by using a PtMn alloy film as antiferromagnetic material of the antiferromagnetic layer. Accordingly, even when the spin-valve film laminate is made up of the increased number of total layers, a total thickness of the spin-valve film laminate is not significantly increased and a reduction in the magnetic gap length can be realized.
In the above magnetoresistive sensors of the present invention, the free magnetic layer and the pinned magnetic layers are made of, e.g., a FeNi (ironxe2x80x94nickel) alloy.
Alternatively, the free magnetic layer and the pinned magnetic layers are made of any of Co (cobalt), a FeCo (ironxe2x80x94cobalt) alloy and a Fexe2x80x94Coxe2x80x94Ni (ironxe2x80x94cobaltxe2x80x94nickel) alloy.